It is desirable at the time an air launched vehicle is being fired, for the rocket motor to quickly accelerate the missile from the launch rail or launch rack, such that a clean separation will be obtained. It is also desirable, as the missile moves ahead of the launching aircraft, for the amount of rocket exhaust, including solid particulates being ingested into the engine of the aircraft, to be minimized.
Somewhat similarly, when dealing with shoulder launched weapons, it is desirable for the pressures and particulate matter effects on the soldier be minimized, and when bringing about the firing of a canister-launched surface-to-air or surface-to-surface missile, it is most important to prevent the condensation of undesirable material on optical and laser windows.
Furthermore, in the launch of certain rocket powered missiles, it is desired to have an initial high mass flow from the rocket motor, followed by a much lower mass flow, with this then being followed by a gradually increasing mass flow until such time as a peak is reached just before motor burnout. The initial high mass flow mentioned above is obviously desirable in order for the missile to have sufficient thrust to clear the launch apparatus. However, previous attempts to attain the desired initial high mass flow usually resulted in the creation of large plumes, which were quite inconsistent with reliable acquisition of the missile by the launcher-mounted guidance equipment, with this latter problem being in addition to certain of the other factors mentioned hereinabove.
The customary approach to the goal of obtaining high initial thrust has been to resort to using a costly motor design that utilizes two different propellent formulations in order to bring about desired thrust characteristics. However, these previous attempts not only exceeded the cost budget, but also created an unusually high amount of particulate matter, that served to degrade the performance of the engine of the launching aircraft, or to jeopardize the well-being of the soldier launching a missile from his shoulder.
In addition, if a separate eject motor concept is utilized in connection with a canister-launched configuration, then the problem exists of either capturing the eject motor, with the attendant capture shock loading on the launcher, or else permitting the eject motor to follow the missile out of the canister, thereby creating a substantial amount of debris around the launcher when the missile motor is ignited.
U.S. Pat. No. 3,951,072 to Baker bears some superficial resemblance to the instant invention in that the patentee disposes an igniter in the forward end of the propellant grain, which igniter is responsible for igniting the main grain. Baker, however, teaches the configuring of his aft main motor propellant grain for the express purpose of keeping high temperature gases from coming into contact with the motor case until very late in the motor burn period. By this configuration, less inert insulative materials are needed to protect Baker's case from overheating and possibly failing under the conditions of the motor operating pressure. In the Baker device, propellant is in effect used in place of the much lower energy of insulation material, resulting in more power being generated in a given motor volume and perhaps even the same total motor weight. In general, the Baker invention simply makes a motor more efficient, i.e., more total impulse per unit weight.
Baker assuredly does not teach the configuring of the main motor grain so that a portion of it, when burned over the same time period as the igniter burn time, produces a large mass flow rate (high thrust) out of the main motor, nor after igniter burn-out does the remaining grain design produce a much lower mass flow rate (lower thrust), nor are these followed by an increasing mass flow rate (higher thrust) to propellant consumption.
Baker thus does not teach nor does he claim the radical and highly desirable change in mass flow rate that forms the bedrock of the present invention. In clear support of this position is the fact that in his Background of the Invention, Baker states " . . . resulting in improved burning with more even power distribution . . . ". That clearly represents a teaching away from the present invention.
Accordingly, it is an important goal of the instant invention to advance the state of the art by bringing about the creation of a rocket motor configuration serving to provide highly desirable thrust characteristic as well as to minimize the problems of the launching aircraft, soldier, or launch canister.